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From: dkraemer@wi.rr.com (dave)
Newsgroups: sci.electronics.design
Subject: Re: off when it's on?
Date: 7 Oct 2002 10:57:00 -0700
Organization: http://groups.google.com/
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NNTP-Posting-Date: 7 Oct 2002 17:57:00 GMT
Terry Pinnell wrote in message news:...
> Do you mean that you want to use the 3914 in dot as opposed to bar
> mode, with the unusual difference that you also want to alternate the
> lit and unlit LEDs? What exactly do you mean by 'when the 3914 is on',
> and '...off'?
>
> Terry Pinnell
> Hobbyist, West Sussex, UK
Im sorry, I didnt want to get to wordy right off the bat.
Im attempting to connect 3 3914. The first one, led 1 - 10, will be
used to indicate vacuum and the other two, led 11 - 30, will indicate
preasure. They will be setup in bar mode.
The preasure transducer puts out a voltage of 1.78volts at 0psi and
voltage drops as vacuum is increased. This makes the first 10 leds
light at 0psi. I want them to be off except when under vacuum. This
would make it work like the zero-center schematic in the spec sheet of
the 3914 without the need for a negative supply.
I think the simplest way of looking at this is when voltage is applied
the led turns off, and when voltage is removed the led turns on. The
rest of the circuit shouldnt be affected, right?
Thanks.
davidk